Radio frequency identification (RFID) technology also known as radio frequency identification tag (RFID tag) is a communication technology for identifying a specific object through an electromagnetic signal by an identification system (such as a reader), as well as reading or writing related data in the specific object, with the advantage of having no mechanical or optical contact between the identification system and specific object at all. Compared with the barcode technology, the RFID tag can store and process a certain quantity of information, and the identification system can exchange information with a RFID tag at a certain data transmission rate through radio signals. Therefore, the RFID tag are used extensively in many areas including:
(1) Anti-counterfeit technology for banknotes and products;
(2) Identity card, pass, and ticket;
(3) Electronic fee collection system, such as Octopus of Hong Kong, and Easycard of Taiwan;
(4) Livestock or wild animal identification; and
(5) Patient identity and electronic medical record.
In general, RFID tags are mainly divided into three types, respectively: passive RFID tags, semi-passive (or semi-active) RFID tags and active RFID tags, and their main properties and differences are listed as follows:
(1) Passive RFID tag: This RFID tag does not come with any internal power supply, and its internal integrated circuit is driven by a received electromagnetic wave, and the electromagnetic wave comes from a reader. If the intensity of an electromagnetic signal received by the passive RFID tag is large enough, data can be transmitted back to the reader.
(2) Semi-passive RFID Tag: This RED tag is similar to the passive RFID tag, except it has a small battery with sufficient electric power for driving the integrated circuit in the tag, setting the integrated circuit at an operating state, and improving the response speed and efficiency of the RFID tag.
(3) Active RFID Tag: Unlike the passive and semi-passive RFID tags, the active RFID tag includes an internal power supply for supplying an electric power source to the internal integrated circuit to generate an external signal. The active RFID tag generally has a longer reading distance and a larger memory capacity for storing additional information transmitted from the reader.
The RFID tag described in the present invention primarily refers to the active RFID tag, and this type of RFID tag is the mainstream product of the present RFID tag market, and has the following advantages:
(1) It provides a greater capacity for storing information;
(2) It provides a longer communication distance;
(3) It requires a higher level of difficulty for duplication;
(4) It has a larger tolerance to environmental changes; and
(5) A reader can read several RFID tags simultaneously.
Due to the aforementioned advantages of the RFID tag, the RFID tag is used extensively in areas of logistics and distribution management for instant monitoring and control of details including production, transportation, allocation, and sales, so that users can control related product information (such as product type, manufacturers, dimensions, quantity, delivery destination and receiver) accurately. With reference to FIG. 1 for a conventional RFID tag 10 available in the market, the RFID tag 10 comprises a transceiver antenna 11, a chip 12 and a substrate 13, wherein the substrate 13 is usually made of a polyimide based material, and the transceiver antenna 11 is installed onto the substrate 13. In general, a copper foil is attached onto the substrate 13 first, and then the transceiver antenna 11 is formed by an etch technology according to a pre-designed antenna pattern. Both ends of the chip 12 are coupled to feed-in terminals of the transceiver antenna 11 respectively, such that the chip 12 can receive or transmit radio signals through the transceiver antenna 11.
When the RFID tag 10 is attached onto a non-conductive object (such as an object made of plastic or glass), the RFID tag 10 still can maintain its normal signal transmission effect to exchange information with a reader within a predetermined range (or distance). However, if the RFID tag 10 is attached onto a surface of a metal object and the transceiver antenna 11 transmits an electromagnetic signal, the metal object will produce an image pulse according to the image theory. The image pulse has a phase opposite to the phase of the electromagnetic signal transmitted from the transceiver antenna 11, and the image pulse and the electromagnetic signal have an offset interference, so that the electromagnetic signal will be damaged and cannot be transmitted to the reader, and the reader will be unable to read the information from the RFID tag 10 properly. The so-called offset interference refers to the condition that the peak of a wave and the trough of another wave reach a location at the same time. When the two waves are overlapped, the resultant wave has an amplitude smaller than the amplitude of the component waves. If the two waves have an opposite-phase interference, then a minimum amplitude will be produced, and such phenomenon is called a fully offset interference.
To keep a delivering item dry, avoid the item from becoming rusty or moldy, or comply with the requirement of the item that cannot be placed in direct sunlight, many existing distribution systems require users (or logistic system manufacturers) to pack the delivering item into a metal bag (such as an aluminum foil bag) for the delivery process. Since the metal bag has the advantages of a high strength, a high tenacity, and a good moisture resistance, therefore the use of metal bags becomes increasingly popular in different logistic systems. However, the aforementioned RFID tag 10 cannot be applied to metal bags due to the image pulse problem. If a user attaches the RFID tag 10 onto a metal bag, the transmission distance of the RFID tag 10 may probably drop to zero, and the reader will be unable to read the RFID tag 10, and the user will be unable to manage each delivering item accurately. Obviously, such application requires improvements.
Therefore, it is an important subject for the present invention to improve the problems of the conventional RFID tag by directly using the metal bag as an antenna of the RFID chip to maintain a good transmission performance.